1. Field of the Invention
The invention relates to a cage unit and a tapered roller bearing equipped with the cage unit. More specifically, the invention relates to a cage unit including a lubrication groove for accommodating lubricating oil, and a tapered roller bearing equipped with the cage unit.
2. Description of Related Art
A tapered roller bearing has been conventionally used to configure a rotation supporting unit of various types of mechanical devices. In such tapered roller bearing, a sliding portion exists between an end face of a tapered roller and a rib end face of an inner ring or an outer ring. A contacting state of both end faces in the sliding portion is a rolling contact that involves sliding. Thus, when the lubricating oil to be supplied to the bearing runs short or runs dry, seizure easily occurs at the end faces.
During the operation of the mechanical device, the lubricating oil is scattered and supplied to the bearing due to the stirring of the lubricating oil, and the like involved in the rotation of a shaft. If the mechanical device is once stopped but immediately re-started, the lubricating oil remaining on both end faces can maintain a lubricating effect, and hence the seizure does not occur.
However, if the mechanical device is once stopped and re-started after a considerable time has elapsed, the lubricating oil attached to both end faces flows down by gravity, and the lubricating oil runs short or runs dry. Thus, the seizure easily occurs.
Forming a groove for oil sump in a cage itself, which holds a plurality of tapered rollers at predetermined intervals along a circumferential direction, has been proposed (see e.g., Japanese Patent Application Publication No. 2007-32612 (JP 2007-32612 A)). FIG. 4A is a partial perspective view of a cage 20 in a roller bearing described in JP 2007-32612 A. FIG. 4B is a partial plan view of the same. In the cage 20 described in JP 2007-32612 A, a circumferential groove 23 that lies along a circumferential direction is formed on an inner end face 21a, which faces a pocket 22, of a large diameter end 21 of the cage 20. The seizure is assumed to be prevented since the shortage of the lubricating oil at the time of an initial operation after a long idle period is alleviated by the lubricating oil accommodated in the circumferential groove 23. In FIGS. 4A and 4B, a reference number 24 denotes a cage bar portion that connects a small diameter end 25 and the large diameter end 21 of the cage 20.
As shown in FIG. 5, the circumferential groove 23 in the roller bearing described in JP 2007-32612 A is formed over the entire inner end face 21a facing the pocket. Thus, portions 23a in the vicinity of both ends of the circumferential groove 23 do not face the end face of the tapered roller 26 and are in an opened state. If an operation stopped state is continued for a long period of time, therefore, the lubricating oil flows out, though only gradually, from the portions 23a in the vicinity of both ends of the circumferential groove 23, whereby the lubricating oil may run short or run dry and the seizure may occur at the time of re-start.